An inkjet printing apparatus is provided with one or more pens or printheads, containing and/or attached to an ink supply; each printhead has a firing chamber from which drops of ink are ejected through a plurality of nozzles towards a printing media, such as paper, in order to form a desired image.
The drops of ink may be ejected from a printhead by several means, e.g. providing a transducer to discharge the ink droplets from the nozzles. This could be done by thermal ink jet technology, or any other.
Amongst other maintenance operations, occasionally it is necessary to prime a printhead by creating a pressure differential that forces an amount of ink from the ink supply through the nozzles.
Priming may be necessary for maintaining or recovering satisfactory operation of the printhead, e.g. for removing ink that has dried on the printhead, or for unclogging or unblocking the nozzles if clogging has occurred; the need for a priming operation is more important with inks having a high concentration of solids, since they tend to clog more easily the printhead nozzles, e.g. pigmented inks.
Priming may be effected by causing the pressure to fall downstream of the nozzles, thus suctioning ink from the ink supply and through the nozzles, or by applying a positive pressure within the ink supply line, e.g. using some kind of pump upstream of the printhead, thus forcing ink through the nozzles.
Known priming methods generally involve the use of devices such as a peristaltic pump, as in U.S. Pat. No. 6,024,433, or a diaphragm driven by a cam, such as described in commonly owned U.S. Pat. No. 5,714,991, or a pump system driven by the horizontal movement of the printer carriage and a manifold system to arrive to each pen, or others. Another priming mechanism is described in commonly owned U.S. Pat. No. 6,419,343. All these solutions are relatively complex and expensive.
Still another known method includes a manually activated system with a bellows; such a solution requires user intervention and depends partly on the skill of the person performing the operation.